Measuring an internal door latch is essential when replacing an old one or installing a new door. The key measurements ensure the new latch fits correctly into the door and aligns with the door handle or knob and the strike plate on the frame.
Key Measurements for Internal Door Latches
According to the provided reference, two critical measurements are used when dealing with internal door latches:
- Backset
- Case Depth
Let's look at how each of these is measured.
Measuring the Backset
The backset is perhaps the most crucial measurement as it determines how far the door handle/knob is from the edge of the door.
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How to Measure: To measure the backset, measure from the edge of the door to the centre of the hole where the latch is fitted. This is specifically the center of the spindle hole where the handle or knob shaft passes through.
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Importance: Matching the backset ensures your new latch works with the existing handle holes in the door. Common backset sizes for internal doors include 44.5mm (1.75 inches) and 57mm (2.25 inches), though others exist.
Measuring the Case Depth
The case depth tells you the overall size of the latch body that fits inside the door mortise (the cut-out area).
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How to Measure: Measure the Case Depth. The case depth is the distance from the front of the faceplate to the back of the latch case. The faceplate is the metal strip visible on the edge of the door when the latch is installed.
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Importance: This measurement ensures the latch body fits snugly into the existing cut-out in the door. Typical case depths often correspond closely to common backsets (e.g., a 64mm case depth often has a 44.5mm backset, and a 76mm case depth often has a 57mm backset), but it's vital to measure both.
Summary Table of Latch Measurements
| Measurement | Description | How to Measure (as per reference) | Purpose |
|---|---|---|---|
| Backset | Distance from door edge to center of spindle hole | Measure from the edge of the door to the centre of the hole where the latch is fitted. | Ensures handle/knob aligns with existing holes. |
| Case Depth | Overall depth of the latch body | Measure from the front of the faceplate to the back of the latch case. | Ensures latch body fits into the door cut-out. |
By accurately measuring the backset and case depth of your existing latch or door preparation, you can select a replacement that fits perfectly, saving time and effort during installation.
